SEOUL, South Korea — An American college student who tearfully apologized for trying to steal a political propaganda poster from his hotel in Pyongyang, the North Korean capital, was sentenced on Wednesday to 15 years of prison and hard labor.

The punishment of the student, Otto F. Warmbier, infuriated the White House and elicited strong condemnations from other officials and rights activists. It came amid rising tensions between North Korea and the United States over North Korea’s unbridled nuclear weapons and missile testing.

Hours later, the Obama administration announced broad new sanctions against North Korean officials and a range of industries in the country, including the shipping, mining, energy and financial service sectors. American officials said the sanctions were an outcome of a new United Nations Security Council resolution imposed on North Korea two weeks ago.

“These actions are consistent with our longstanding commitment to apply sustained pressure on the North Korean regime,” the White House said in a statement.

Mr. Warmbier, 21, a University of Virginia undergraduate from the Cincinnati area, was convicted after a one-hour trial Wednesday morning at North Korea’s Supreme Court, news services in Pyongyang reported. A clip from state television showed Mr. Warmbier, head down and hands shackled, as he was escorted by two officers in and out of court.

The sentence was the latest in a series of penalties that the government has meted out to a small number of American tourists, missionaries and journalists in recent years for what have been deemed antistate crimes, including accusations of illegal entry and leaving a Bible behind in a hotel.

But even by North Korea’s standards, the punishment for Mr. Warmbier appeared to be extreme for an act that might amount to a harmless misdemeanor elsewhere. The Obama administration, along with Mr. Warmbier’s other American supporters and rights activists, denounced the sentence.

Josh Earnest, the White House press secretary, said that it was “increasingly clear that the North Korean government intends to use these citizens as pawns,” and that Mr. Warmbier’s arrest demonstrated why it was hazardous to visit North Korea.

The State Department strongly discourages Americans from traveling to the country, but it is not illegal to do so.

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Gov. John Kasich of Ohio, a Republican candidate for president, said in a statement on his website that Mr. Warmbier’s detention “was completely unjustified and the sentence North Korea imposed on him is an affront to concepts of justice.”

Mr. Kasich, who has spoken with Mr. Warmbier’s parents and has repeatedly called on North Korea to free Mr. Warmbier, said in the statement that “continuing to hold him only further alienates North Korea from the international community.”

Phil Robertson, the deputy Asia director for Human Rights Watch, said that the punishment of “15 years’ hard labor for a college-style prank is outrageous and shocking.”

Mr. Warmbier’s punishment was announced less than a day after Bill Richardson, a longtime American diplomat and former governor of New Mexico who has visited Pyongyang a number of times, met with two North Korean officials in New York to urge Mr. Warmbier’s release on humanitarian grounds.

Mr. Richardson, who had been asked by Mr. Kasich to become involved in the case because of his experience in dealing with North Korea, suggested that the punishment should not necessarily be taken at face value.

“An unfortunate development but a familiar pattern with American detainees,” Mr. Richardson said in an email. “Hopefully a prelude to negotiations that might lead to a release on humanitarian grounds.”

Mr. Warmbier, who entered North Korea as part of a tour group, was detained on Jan. 2 as he was about to board a plane to leave the country. In announcing his arrest, the state news media said that Mr. Warmbier had visited with the intent of “bringing down the foundation of its single-minded unity.”

The charges against him claimed that the C.I.A., a secretive American university organization and a member of a church in Ohio had encouraged him to commit the “hostile act” of stealing a political poster from a wall in his hotel.

Late last month, Mr. Warmbier sobbed and pleaded for his release at a government-arranged news conference in Pyongyang, where he admitted stealing the poster and said that the church member had offered to buy him a used car worth $10,000 in exchange. “I made the worst mistake of my life,” Mr. Warmbier said.

It was impossible to determine whether Mr. Warmbier had been coerced into making the statements. Some American detainees who have spoken at similar news conferences in Pyongyang later said, after being freed, that they had been forced to confess to crimes and to apologize.

A version of this article appears in print on March 17, 2016, on Page A8 of the New York edition with the headline: North Korea Gives U.S. Student a 15-Year Sentence. Order Reprints|Today's Paper|Subscribe